For it will be seen that if the spectator on the globe, when in the position that its inclined axis, as shown in Fig. 5, points towards the sun, were looking at the sun from a place where one can imagine England to be at midday, the sun would appear to be very high up above the horizon; and if he looked at it from the earth in the opposite part of its orbit it would be very low and near the horizon. When the earth, therefore, occupied the intermediate positions, the sun would be half way between the extreme upper position and the extreme lower position as the earth moves round the sun, and in this way the solstices, equinoxes, and the seasonal changes on the surface of our planet, are easily explained. ----- Footnote 1: Corresponding to 20th July, 139 B.C. Footnote 2: Anaximander flourished about 547 B.C. Footnote 3: Quoted by Sir G. C. Lewis in his _Astronomy of the Ancients_, p. 187. CHAPTER II. THE FIRST INSTRUMENTS. The ancients called the places occupied by the sun when highest and lowest the Solstices, and the intermediate positions the Equinoxes. The first instrument made was for the determination of the sun’s altitude in order to fix the solstices. This instrument was called the Gnomon. It consisted of an upright rod, sharp at the end and raised perpendicularly on a horizontal plane, and its shadow could be measured in the plane of the meridian by a north and south line on the ground. Whenever the shadow was longest the sun was naturally lowest down at the winter solstice, and _vice versâ_ for the summer solstice. Here then we leave observations on the horizon and come to those made on the meridian. The Gnomon is said to have been known to the Chinese in the time of the Emperor Yao’s reign (2300 B.C.), but it was not used by the Greeks[4] till the time of Thales, about 585 B.C., who fixed the dates of the solstices and equinoxes, and the length of the tropical year—that is, the time taken by the sun to travel from the vernal equinoctial point round to the same point again. The next problem was to discover the inclination of the ecliptic, or, what is the same thing, the amount that the earth’s equator is inclined to the ecliptic plane (represented by the surface of the water in our tub). Now in order to ascertain this, the angular distance between the positions occupied by the sun when at the solstices must be measured; or, since one solstice is just as much below the equinoctial line as the other is above it, we might take half the angle between the solstices as being the obliquity required.